Hi Brom, you’re right the feet certainly look pale on the photo. The Handbook of Western Palearctic Birds states that leg colour only distinguishes 75% of Common Chiffchaff from Willow Warbler. It goes onto say that both collybita and abietinus subspecies of Chiffchaff occasionally have “paler legs, brown rather than blackish, in practice very like Willow Warbler and inviting confusion”. This bird was displaying typical tail-dipping and call of Common Chiffchaff and was in the garden again today but I didn’t have my camera available and am reluctant to disturb it.
It would be interesting to know where it was last summer, the BBC’s Winterwatch recently said that wintering ones here may come from Scandinavia. If anyone has a theory if this individual could be abietinus then it would be interesting to hear.